The present invention relates generally to photosensitive structures and more particularly to a photosensitive, unilayer, film structure suitable for use in the manufacture of water-processable printing plates and other graphic arts elements.
Many different photosensitive systems are well-known in the art for the manufacture and preparation of lithographic plates. Diazo compounds are, of course, frequently used as the photosensitive component in such systems. The diazo compounds can be formulated to possess several assets which make them desirable for use in this field, including low-cost, long shelf-life, water solubility, and good photosensitivity. However, the ink receptivity of diazo compounds is seriously reduced when they are contacted by water and the inherent durability of diazo resins is relatively low. Accordingly, approaches to the manufacture and preparation of printing plates utilizing diazo compounds have sought to overcome this problem by using lacquer-based developers, or overcoating the diazo with an ultra-violet transmitting lacquer or other material. These approaches, while enjoying some success, result in the loss of the simple water processing of the diazo compound plates and in some instances have required increased exposure times. Moreover, diazo compounds lack sufficient bond strengths to smoother substrates and therefore it has been necessary to provide grained substrate surfaces to increase the mechanical bonding of these photosensitive coatings, in order to achieve useful lengths of press runs.
Another popular photosensitive system employs photopolymers which have both high ink receptivity and durability. These systems, however, generally require special solvents to develop the plate, thereby increasing system complexity compared to simple water processing and, in addition, presenting undesirable ecological waste problems.